It is known to dry high moisture-containing coals by heating the coal in a coal-oil slurry form prior to further processing steps such as liquefaction. For example, U.S. Pat. Nos. 3,396,099 to Glinka, 3,519,552 to Hellwig, and 3,680,217 to Chapman disclose drying wet coal to remove moisture by contacting it with hot slurrying oil. Also, 3,520,067 to Winegartner shows such a process for drying wet crushed coal in which the water is vaporized by heating the coal in an oil slurry heated with steam in an elongated vessel, with the resulting water vapor evaporated from the coal being withdrawn off the top of the vessel.
Considerable heat is required in the dryer to evaporate substantially all the moisture from the coal-oil slurry mixture to permit its further processing, such as in a coal liquefaction step, without encountering undesirable operating problems due to its remaining moisture content. Also, it is very desirable to dry such coal under non-oxidizing conditions in order not to oxidize or reduce the heating value of the coal before passing it on to a liquefaction step. Furthermore, it would be desirable to provide such heat to the coal dryer in an efficient manner, such that all or a major portion of the heat available from the vaporized steam is utilized in the process, and the water produced is available for reuse elsewhere in the system.